Fossilization of organic matter, formation of oil and gas, and emigration of hydrocarbons in carbonate rocks

Abstract

Based on the comparison of conditions of organic matter (OM) accumulation in modern carbonate sediments in Paleozoic shallow-water carbonate sediments, it is shown that drastic disproportion in the degree of preservation of the primary dispersed OM (DOM) in the clayey and “pure” varieties of carbonate rocks is not caused by its loss due to the diagenetic oxidation in the shallow-water setting, its disintegration due to the vital activity of microorganisms, or due to its consumption for the reductive oxide forms of Fe. It has experimentally been proven that a great significance in oil and gas formation in carbonate rocks belongs to OM, which occurs in the carbonate component of the chloroform bitumen (CB_CCR) and is not determined by the conventional analytical methods (e.g., incineration of the HCl-insoluble rock remnant). Higher concentration of hydrocarbons (HC) in CB_CCR relative to CBA is confirmed by the oil-generating properties of “pure” carbonate rocks. The release and emigration of HC from carbonate rocks are promoted by their secondary transformations.